It's what we call a "noisy" unit. It means that the computer finds so many pulses, gaussians and trplets in the first minute that it won't be able to store all of that in a unit on the drive. It will then stop crunching and send the unit back. You still do claim a small portion of credits for the time that this unit was crunched.

It's for the developers to look into this unit to see what could be causing this amount of noise.